As a flat display device in which emission from gas discharge is utilized, a plasma display panel, which will be referred to as PDP hereinafter, has been conventionally come into the market. Concerning PDP, two types are provided. One is a DC type and the other is an AC type. As a large display device, a face discharge type AC type PDP has a higher technical potential and provides long life. Therefore, the face discharge type AC type PDP has been put on the market.
FIG. 7 is a sectional view showing a structure of a discharge cell of a conventional face discharge type AC type plasma display panel. As shown in FIG. 7, on first substrate 1 which is a front plate of the discharge cell, a pair of transparent electrodes (not shown) are formed on a surface of glass substrate 2 while discharge gap g1 of about 80 μm is being interposed between the pair of transparent electrodes. Bus electrodes (not shown), which are formed out of metallic electrodes so as to reduce electric resistance, are respectively formed on the pair of transparent electrodes. In this way, a plurality of pairs of display electrodes 5 are formed which includes first electrode 3, which is a scanning electrode, and also includes second electrode 4 which is a maintaining electrode. Dielectric material layer 6 and protective film 7 are successively laminated to cover the pair of electrodes. Dielectric material layer 6 is made of glass, the melting point of which is low. Dielectric material layer 6 has an electric current limiting function which is peculiar to AC type PDP. Protective film 7 protects surfaces of the above pair of electrodes and effectively emits secondary electrons so that the discharge starting voltage can be lowered. Concerning the material of protective film 7, metallic oxide MgO (magnesium oxide) is widely used which is an optically transparent electric insulating material, the secondary electron emission coefficient γ of which is high and further the spattering resistance of which is high.
On the other hand, on glass substrate 9 of second substrate 8 which is a back plate, third electrode 10, which is a data electrode for writing down image data, is formed in a direction perpendicular to the direction of display electrode 5 of first substrate 1. Further, dielectric layer 11 on the back side is formed out of glass, the melting point of which is low, so that at least portions of the surfaces of third electrode 10 and glass substrate 9 can be covered. On dielectric material layer 11 in a boundary with an adjoining discharge cell (not shown), bulkhead 12, the height of which is predetermined, is formed out of glass, the melting point of which is low, for example, into a pattern shape, such as a stripe shape or a parallel cross shape. Further, on a surface of dielectric material layer 11 and on a side of bulkhead 12, fluorescent material layer 13 is formed. On fluorescent material layer 13, fluorescent materials of emitting three colors of red, green and blue are formed in the corresponding discharge cells.
Worked faces of first substrate 1 of the front plate and second substrate 8 of the back plate are opposed to each other. First electrode 3 and second electrode 4 are arranged so that they can cross third electrode 10 while making a right angle with third electrode 10. In this way, these components are tightly sealed on the panel. After the atmosphere and impure gas are discharged from the panel, Xe (xenon) mixed gas such as xenon.neon or xenon.helium, which is rare gas, is charged and sealed on the panel as discharging gas by the pressure of several tens kPa.
On the plasma display panel on which a plurality of discharge cells are arranged being formed into a matrix, a drive circuit for driving like a matrix and a control circuit for controlling the drive circuit are provided. In this way, the plasma display device is composed.
In the conventional PDP shown in FIG. 7, the maintaining discharge, which is a primary discharge for ensuring the luminance, is “a face discharge” generated between first electrode 3 of the scanning electrode and second electrode 4 of the maintaining electrode which are an anode and cathode formed substantially parallel with the surface of glass substrate 2. That is, an angle, which is formed between an electric line of force in the discharge space and the surface of protective layer 7 contributing to discharge, is extended to be large length. Accordingly, a loss of charged particles and excited particles at the time of discharging is increased. Accordingly, the discharge starting voltage becomes necessarily higher than “the opposition discharge voltage” at the time of the same discharge gap. In this case, “the opposition discharge” is defined as a discharge in which an angle formed between the electric line of force in the discharge space and the electrode face contributing to discharge is small. Since the discharge is PDP of a narrow gap length in which the discharge gap is small, discharge region 14 is small. Therefore, the light emission efficiency is low and it is difficult to increase the luminance.
In order to solve the above conventional problems, Japanese Patent Application No. 2000-571429 discloses the following PDP of high luminance. When the discharge gap formed by the display electrode including the first and the second electrode is made long, the discharge region is extended to be larger than that of the conventional discharge region. Therefore, the light emission efficiency is enhanced by 1.5 times.
FIG. 8 is a sectional view showing a structure of another example of a discharge cell of a conventional face discharge type AC type plasma display panel. Like reference numerals are used to indicate like parts in FIGS. 7 and 8.
As shown in FIG. 8, display electrode 15 of first substrate 1, which is a front plate of the discharge cell, is arranged on a surface of glass substrate 2 in such a manner that, for example, while discharge gap g2, which is a long gap of 200 to 300 μm length, is being interposed between first electrode 16 and second electrode 17, which are formed out of metallic electrodes, when first electrode 16 and second electrode 17 are formed by a narrow width.
When display electrode 15, the discharge gap of which is formed to be long, is provided in this way, first, discharge is generated in the longitudinal direction between first electrode 16 and third electrode 10 which is a data electrode, because an interval between first electrode 16 and third electrode 10 is small. Next, face discharge is generated between first electrode 16 and second electrode 17 having a long gap upon which high maintaining discharge voltage of about 300 V is impressed. Due to the foregoing, the discharge region is extended and the light emission efficiency is enhanced and the luminance is increased high.
However, the discharge starting voltage of PDP of the above long gap becomes higher than the discharge starting voltage of the conventional PDP of the narrow gap described before. The reason why the drive voltage is increased is described below. In the same manner as that of the narrow gap PDP, even in PDP of a long gap, an electric line of force, which is generated between the electrodes arranged in parallel with the substrate face, obliquely comes out from the electrode face. Therefore, the discharge form is “a face discharge”. Since the gap length is increased, the discharge staring voltage is necessarily raised as compared with the discharge starting voltage of PDP of a narrow gap.
In order to solve the above problems, for example, the official gazette of Japanese Patent Unexamined Publication No. 2003-132804 discloses the following technique. When a display electrode is formed on a face of a side portion of a bulkhead, a principal plane contributing to discharge on the display electrode is made to cross with the substrate face while making a substantially right angle. An opposition discharge, which is generated between a principal plane of the adjoining electrode and a principal plane which is arranged being opposed to the principal plane of the adjoining electrode via a discharge space, is made to be a maintaining discharge. Due to the foregoing, the discharge region is extended and the light emission efficiency is enhanced. The discharge form of this example is an opposition discharge between electrodes interposing the discharge gas space. In this case, an electric charge movement direction is not a direction of the panel thickness but a direction along the substrate face. This discharge form is referred to as “a face direction opposition discharge”.
When an electric power supply portion formed out of a conductive film provided on the display electrode is formed on a surface of the side of the bulkhead formed on the front face plate, a principal plane contributing to discharge from the display electrode is made to cross with the substrate face while making a substantially right angle and arranged being opposed to the principal plane of the adjoining display electrode while interposing a gas space. Further, on the front plate, in order to cause pilot light discharge, a pair of auxiliary electrodes are provided between the pair of display electrodes.
In the conventional face discharge type AC type PDP, the gap of which is narrow, the maintaining discharge is a face discharge. Therefore, a great loss is caused in the discharge and the discharge starting voltage is raised. Further, due to the narrow gap, the discharge region is small. Therefore, the light emission efficiency is low and it is difficult to enhance the luminance.
When it is made to be an AC type PDP, the gap of which is long, the light emission efficiency is enhanced and the high luminance can be obtained. However, in the same manner as that described above, the maintaining discharge becomes a face discharge. Therefore, the discharge starting voltage is raised. When the gap is extended long, it becomes necessary to provide a higher maintaining discharge voltage of about 300 V. Since the drive voltage is raised, a peak value of the discharge electric current is increased. Especially, in the case of a large image plane panel, it is difficult to sufficiently supply a sharp and high peak electric current. Accordingly, a state of discharge in each discharge cell greatly depends upon a lighting area of the panel. Accordingly, a large image plane driving display becomes not uniform.
On the other hand, in the case where a discharge region is extended by making the maintaining discharge, which is conducted between the display electrodes, to be a face direction opposition discharge when an electric power supply portion of the display electrode is formed on a surface of the side of the bulkhead formed on the front plate, the opposition discharge is conducted, so that the discharge region can be extended and the light emission efficiency can be enhanced. However, since an auxiliary electrode is provided in addition to the display electrode in this case, the opening ratio is deteriorated and the luminance is lowered. Further, this structure is complicated in such a manner that a bulkhead is formed on the front plate and an electric power supply portion, which is extended from the display electrode, is formed on a surface of the bulkhead side portion as a principal plane of the display electrode and opposed. Therefore, it is difficult to manufacture the device and the manufacturing cost is raised.